This revised renewal application is to continue studies of the role of peroxiredoxin 6 (Prdx6) in antioxidant defense. The focus during the coming grant period will be on the role of Prdx6 in the repair of peroxidized membrane phospholipids following oxidant stress. Theoretically, membrane repair can occur through two processes, direct reduction of peroxidized phospholipid (PLOOH) or a remodeling pathway requiring the sequential activity of phospholipase A2 (PLA2) and lysophospholipid acyl transferase (LPAT). We have shown previously that Prdx6 expresses both the ability to reduce PLOOH by a peroxidase activity utilizing glutathione as well as a PLA2 activity, and that both of these activities play an important role in resistance to oxidative stress in lung cells. We have recently discovered that Prdx6 also expresses LPAT activity. Therefore, Prdx6 has all three activities (peroxidase, PLA2, LPAT) that are assumed to be required for repair of peroxidized cell membranes. As the LPAT activity of Prdx6 is as yet undescribed in the literature, we will investigate the properties and regulation of this novel enzymatic activity. It is proposed that the repair of membrane lipid peroxidation is a key determinant for cell survival associated with oxidant stress and that Prdx6 expressing its 3 important activities plays a crucial role. We have developed mouse models that are Prdx6 null or, through knock-in technology, express either the peroxidase or the PLA2/LPAT activities of Prdx6 and we have isolated mutant cells from their lungs. Additional mutants will be generated by lentivirus infection of Prdx6 null cells. We will study oxidant stress in isolated lung cells (alveolar type II epithelial, alveolar macrophages microvascular endothelial cells), isolated perfused lungs, and intact mice in order to determine the requirement for Prdx6 in repair of peroxidized lung cell membranes and the relative roles of the direct reduction and the reacylation pathways. Lipid peroxidation in lungs and lung cells will be measured by mass spectroscopy or biochemical assay and repair will be determined following removal of the oxidant stress. The stressors will be tert-butyl hydroperoxide or Cu2+/ ascorbate for lungs and cells and hyperoxia for mice. We also will administer bleomycin to mice to investigate the relationship of membrane repair following acute oxidant stress to the subsequent development of lung fibrosis. These studies should provide important novel information related to recovery of lungs from oxidative stress and could lead to therapeutic modalities to augment the recovery process.